There are several variables to optimize for LED performance in LED lighting or LED displays, for example, color quality and power conversion efficiency.
The metric for color quality is Color Rendering Index (CRI). A perfect blackbody radiator is used as a basis for the CRI calculation. As such, a blackbody radiation spectrum has the highest possible CRI value of 100. However, a blackbody radiator has a considerable amount of emitted power in regions to which the human eye is not sensitive. To obtain an optimal CRI, the blackbody radiation spectrum is truncated to the human-visible range of the spectrum. However, the particular blackbody spectrum is dependent on the temperature of the blackbody, which is known as the Correlated Color Temperature (CCT).
A primary metric for power conversion efficiency is Luminous Efficacy of Radiation (LER). The goal in efficient lighting design is to optimize the amount of electrical power that is converted into light energy. However, the human eye is more sensitive to some wavelengths of light compared to other wavelengths of light, being the most sensitive in the green range (approximately 495 nm-570 nm) of the visible spectrum (approximately 380 nm-780 nm). This means a given amount of light can be perceived as having different intensities depending on the wavelength of that light. In order to achieve the highest possible LER, all emitted light should match the peak sensitivity of the human eye (that is, light in the green range).
In order to balance these various parameters, lighting designers attempt to simultaneously optimize both the CRI and LER for a given CCT value. In prior art LED lighting, this may be done through the use of down-conversion conventional phosphors (i.e., Cerium doped: Yttrium Aluminum Garnet (Ce:Yag-Y3Al5O12))—materials that convert blue light to redder (lower energy) wavelengths. While there are many such phosphors available, their emission profiles are broad and are generally not tunable. These limitations mean that many desired theoretical emission profiles simply cannot be realized with these materials. What is needed are quantum dot down-conversion phosphor materials that are both tunable and have a narrow spectral emission profile, meaning that almost any desired emission spectrum can be created through the use of these materials. Such materials would represent a major advance in LED lighting in that any theoretical optical emission spectrum may be readily realized, thus removing the limitations presented by conventional phosphor materials.